[Rd] x <- 1:2; dim(x) <- 2? A vector or not?
Martin Maechler
maechler at stat.math.ethz.ch
Sat Jan 17 22:27:45 CET 2009
>>>>> "TP" == Tony Plate <tplate at acm.org>
>>>>> on Fri, 16 Jan 2009 13:10:04 -0700 writes:
TP> Martin Maechler wrote:
>>>>>>> "PatB" == Patrick Burns <pburns at pburns.seanet.com>
>>>>>>> on Tue, 13 Jan 2009 17:00:40 +0000 writes:
>>>>>>>
>>
PatB> Henrik Bengtsson wrote:
>> >> Hi.
>> >>
>> >> On Mon, Jan 12, 2009 at 11:58 PM, Prof Brian Ripley
>> >> <ripley at stats.ox.ac.uk> wrote:
>> >>
>> >>> What you have is a one-dimensional array: they crop up
>> >>> in R most often from table() in my experience.
>> >>>
>> >>>
>> >>>> f <- table(rpois(100, 4)) str(f)
>> >>>>
>> >>> 'table' int [, 1:10] 2 6 18 21 13 16 13 4 3 4 - attr(*,
>> >>> "dimnames")=List of 1 ..$ : chr [1:10] "0" "1" "2" "3"
>> >>> ...
>> >>>
>> >>> and yes, f is an atmoic vector and yes, str()'s notation
>> >>> is confusing here but if it did [1:10] you would not
>> >>> know it was an array. I recall discussing this with
>> >>> Martin Maechler (str's author) last century, and I've
>> >>> just checked that R 2.0.0 did the same.
>> >>>
>> >>> The place in which one-dimensional arrays differ from
>> >>> normal vectors is how names are handled: notice that my
>> >>> example has dimnames not names, and ?names says
>> >>>
>> >>> For a one-dimensional array the 'names' attribute really
>> >>> is 'dimnames[[1]]'.
>> >>>
>> >>
>> >> Thanks for this explanation. One could then argue that
>> >> [1:10,] is somewhat better than [,1:10], but that is just polish.
>>
>> yes. And honestly I don't remember anymore why I chose the
>> "[,1:n]" notation. It definitely was there already before R
>> came into existence, as S also has had one-dimensional arrays,
>> and I programmed the first version of str() in 1990.
>>
PatB> Perhaps it could be:
>>
PatB> [1:10(,)]
>>
PatB> That is weird enough that it should not lead people to
PatB> believe that it is a matrix. But might prompt them a
PatB> bit in that direction.
>>
>> Well, str() was always aimed a bit at experienced S (and R)
>> users, and I had always aimed somewhat to keep it's output
>> "compact". I'm quite astonished that the OP didn't know about
>> 1D arrays in spite of the many years he's been using R.
>> Would a wierd solution like the above have helped?
>>
>> At the moment, I'd tend to keep it "as is" if only just for
>> historical reminescence, but I can be convinced to change the
>> current "tendency" ...
>>
>> Martin Maechler, ETH Zurich
>>
TP> What about just including "(1d-array)", something like this
>> str(f)
TP> 'table' int [1:10](1d array) 5 5 9 23 26 16 9 4 2 1
TP> - attr(*, "dimnames")=List of 1
TP> ..$ : chr [1:10] "0" "1" "2" "3" ...
>>
TP> only 9 extra characters for a rare case, and much, much less cryptic?
well,.. the next text request is to use
"character" instead of "chr", only 6 extra characters ....
-> no way: str() has its very concise "style" and should keep
that.
Martin
TP> -- Tony Plate
>>
>>
PatB> Patrick Burns patrick at burns-stat.com +44 (0)20 8525
PatB> 0696 http://www.burns-stat.com (home of "The R
PatB> Inferno" and "A Guide for the Unwilling S User")
>> >> /Henrik
>> >>
>> >>
>> >>> I think these days we have enough internal glue in place
>> >>> that an end user would not notice the difference (but
>> >>> those working at C level with R objects may need to
>> >>> know).
>> >>>
>> >>> On Mon, 12 Jan 2009, Henrik Bengtsson wrote:
>> >>>
>> >>>
>> >>>> Ran into the follow intermediate case in an external
>> >>>> package (w/ recent R v2.8.1 patched and R v2.9.0
>> >>>> devel):
>> >>>>
>> >>>>
>> >>>>> x <- 1:2 dim(x) <- 2 dim(x)
>> >>>>>
>> >>>> [1] 2
>> >>>>
>> >>>>> x
>> >>>>>
>> >>>> [1] 1 2
>> >>>>
>> >>>>> str(x)
>> >>>>>
>> >>>> int [, 1:2] 1 2
>> >>>>
>> >>>>> nrow(x)
>> >>>>>
>> >>>> [1] 2
>> >>>>
>> >>>>> ncol(x)
>> >>>>>
>> >>>> [1] NA
>> >>>>
>> >>>>> is.vector(x)
>> >>>>>
>> >>>> [1] FALSE
>> >>>>
>> >>>>> is.matrix(x)
>> >>>>>
>> >>>> [1] FALSE
>> >>>>
>> >>>>> is.array(x)
>> >>>>>
>> >>>> [1] TRUE
>> >>>>
>> >>>>> x[1]
>> >>>>>
>> >>>> [1] 1
>> >>>>
>> >>>>> x[,1]
>> >>>>>
>> >>>> Error in x[, 1] : incorrect number of dimensions
>> >>>>
>> >>>>> x[1,]
>> >>>>>
>> >>>> Error in x[1, ] : incorrect number of dimensions
>> >>>>
>> >>>> Is str() treating single-dimension arrays incorrectly?
>> >>>>
>> >>>> What does it mean to have a single dimension this way?
>> >>>> Should it equal a vector? I am aware of "is.vector
>> >>>> returns FALSE if x has any attributes except names".
>> >>>>
>> >>>> /Henrik
>> >>>>
>> >>>> ______________________________________________
>> >>>> R-devel at r-project.org mailing list
>> >>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>> >>>>
>> >>>>
>> >>> --
>>
>>>> Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied
>>>>
>> >>> Statistics, http://www.stats.ox.ac.uk/~ripley/
>> >>> University of Oxford, Tel: +44 1865 272861 (self) 1
>> >>> South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG,
>> >>> UK Fax: +44 1865 272595
>> >>>
>> >>> ______________________________________________
>> >>> R-devel at r-project.org mailing list
>> >>> https://stat.ethz.ch/mailman/listinfo/r-devel
>> >>>
>> >>>
>> >>
>>
>>> ______________________________________________
>>>
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>> >> https://stat.ethz.ch/mailman/listinfo/r-devel
>> >>
>> >>
>> >>
>>
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